The motor looks like a great one but there has not been a lot of evolution on developing it's use and/or popularity. It is being mean to me, every time I touch it something stupid happens to take all of the fun out of things...

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I actually was intending to post so I could ask about a good source for replacement bearings and shafts for these motors, but I did some more browsing in the thread and saw the link pointing to HeadsupRC. Is that still the go-to place for these supplies? C-clips also?

Brushless motors are so cool- with a supply of bearings and shafts, you can pretty much keep them going forever.

Rick

Heads Up is good for shafts and clips when they have what you need, this motor uses the MR74ZZ 4x7x2.5mm (ID x OD x W) bearing which they don't carry.

An eBay search for "bearing 4 7 2.5" will surface many more hits. These are undersize and overstressed before we do anything stupid even. You can't have too many on hand and you need to lube the bearings before you install them.

On eBay you can usually find the MR74-2RS bearing that has rubber shields on both sides. I like those because they can be filled with lube and it stays in better (I vacuum pack them full). The rubber shields have more drag so it will cost you about 2 RPM for every 10,000 or so. Or maybe 1/10,000ths of a Watt...

Jack

I know metal working and fits and material so I buy shafts from other places (drill blanks for example) when I can't find them anywhere else.

It seems to me that people are just using any old 4mm diameter shaft and modifying them as needed, ie cutting out grooves for circlips and flats for grub screws. If you want a threaded 4mm shaft that's similar to the stock DT, I've read somewhere that people have salvaged them from GWS size 400 power systems but I've no idea what that means or where to even source the part.

Why use a threaded shaft? It is an invitation to having a bent shaft. I am firmly, 100% committed to prop savers and it is one kind of prop saver and using only the world's best prop saver band material, Thera-Band elastic tubing, the how to is here:

[/QUOTE]I've managed to remove my thread locked grub screws by finding a properly sized 1.5mm hex driver. Since I don't know anything about motors, I'm listing my findings on its construction for reference to other complete newbies and confirmation from others.

The pieces along the shaft are ordered as follows:
[circlip]-[1-3 washers*]-[bearing #1]-[stator]-[bearing #2]-[washer]-[bell/rotor]

* I say 1-3 washers because I'm seeing various different washers in the 5 DT700s I have. In some cases, there's 3 equally sized thin washers, or a single fat washer, or a thin washer with a medium washer...[/QUOTE]

The reason for all of those spacers is to get the assembly right when they are taking parts out of bins and hoppers in a mass production shop. It you fit the shaft yourself you can usually eliminate most of those unless they serve a purpose.

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I've assessed the damage, and I think I should be able to salvage 3 of the 4 motors. One is fine as is, and the other two have damaged shafts. The fourth one has a chipped magnet on the rotor and the bell seems to have been slightly deformed enough that it won't spin freely on any of the stators I have.

Picture of three salvageable motors. <images snipped> The bottom one is fine, the top two have damaged shafts. Notice that the top motor also had the shaft pressed further into the bell housing in the crash. You can tell by the shortened amount of unthreaded shaft sticking out compared to the other two motors.

Rotor with chipped magnet

Bonus picture of the motor mount that took the brunt of the fall.

At this point I'm thinking I can take the shaft from the fourth motor and swap it out for one of the motors that has a damaged shaft, likely the top most motor in my first image since that one took the most damage. How do people typically remove the shafts from outrunners? From this thread it seems an arbor press is used. I don't have access to an arbor press nor do I have the space for one in my home, but I think I might be able to use a drill press as an arbor press in conjunction with a bench vise to pull the shafts out. edit: This thread has an excellent method requiring just a vise and a shaft larger than the motor shaft to push against. I'm gonna go to the hardware store and find a pvc pipe for this.

Those threads are pretty much all you need to know to get those apart. The shaft is a moderate force press fit into the magnet housing and held there by a grub screw bearing on a flat on the shaft. The shaft should slide out of the bearing races with light pulling forces. But the snap ring grooves will snag and then more force is needed. And it is hard to restrain the back half (stator and bearing tube) and get a pulling force on the magnet housing.

I use socket wrenches, small pieces of metal tubing, etc. (large enough to take the 4mm shaft), to press the shaft into and through the magnet housing. The tube has to be used to localize the pressing forces to right around the shaft or the magnet housing will be deformed. Aluminum, copper, or brass tubes or pipes are best as you don't have to fight the magnets to use them inside the housing.

I do a lot of my pressing in the horizontal plane with a bench vise. And I'll use punches, smaller shafts, and hammers to make things move when I have to. If the bearings are already shot, I don't worry about damaging them any worse.

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I'm also concerned that for the two motors with bent shafts, they don't seem to spin as freely as the motor that took no damage. When I spin the motor by hand, there's a slight ratchet but it still spins pretty easily. The other two motors are a bit stiffer, and seem to come to a stop quicker if I give the rotor a good spin. I don't think it's the bearings since I've swapped the stators into my spare DT700 and had it spin freely, so I'm thinking the bell must have gotten deformed enough in the crash to cause the magnets to rub up against the stators arms.

The magnets keep the motors from spinning freely but other things can do it too.

On the motors with bent shafts I would try to remove the magnet housings and then cut the bent shafts off with an abrasive disc. Cut them right below the threads and push them down into the housings and out.

Put a tube or deep socket up inside the housing and press the shaft down into it using a smaller than 4mm screw or shaft when it get flush with the housing.

Friendly advice, go to the Advanced posting mode and use the Manage Attachments menu to upload your images to the servers here. That means they will display as thumbnails until click on and also be here forever to help others.

The reason for all of those spacers is to get the assembly right when they are taking parts out of bins and hoppers in a mass production shop. It you fit the shaft yourself you can usually eliminate most of those unless they serve a purpose.

I figured it was something like that. I'm guessing the purpose of the washers is to minimize play in the event that bearing #1 slips out?

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Those threads are pretty much all you need to know to get those apart. The shaft is a moderate force press fit into the magnet housing and held there by a grub screw bearing on a flat on the shaft. The shaft should slide out of the bearing races with light pulling forces. But the snap ring grooves will snag and then more force is needed. And it is hard to restrain the back half (stator and bearing tube) and get a pulling force on the magnet housing.

I use socket wrenches, small pieces of metal tubing, etc. (large enough to take the 4mm shaft), to press the shaft into and through the magnet housing. The tube has to be used to localize the pressing forces to right around the shaft or the magnet housing will be deformed. Aluminum, copper, or brass tubes or pipes are best as you don't have to fight the magnets to use them inside the housing.

I do a lot of my pressing in the horizontal plane with a bench vise. And I'll use punches, smaller shafts, and hammers to make things move when I have to. If the bearings are already shot, I don't worry about damaging them any worse.

Yeah I've been using a 1/2" diameter piece of pvc pipe that's longer than the shaft pressed against the front (propeller) side to help coax the shaft out. This way only a short length of shaft has to bear the strain of being squeezed in the vise. I had problems doing it the other way around, with the pvc pipe on the back end of the housing. My shaft was bending as I compressed the vise due to its full length providing a better torque arm to bend itself with. Of course, this shouldn't have happened to begin with if I hadn't been so eager to fly that I skipped over cutting the shafts down to a proper length.

So now that I've got the shaft flush against the housing, I need to find a tube that's <4mm to push the final bit of shaft out.

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Friendly advice, go to the Advanced posting mode and use the Manage Attachments menu to upload your images to the servers here. That means they will display as thumbnails until click on and also be here forever to help others.

I figured it was something like that. I'm guessing the purpose of the washers is to minimize play in the event that bearing #1 slips out?

Actually it is more about getting the magnets centered over the stator arms.

The housing will "find" that position by itself unless the drag on the shaft in the bearings is too high. If you let the housing center itself will be a small distance between the edge of the housing (where the ends of the magnets are seen) and the bare end of the stator arm. Normally the stator ends are just slightly (.010" or so) lower than the rim of the housing.

With the mousing centered like that, the shaft and mounted Circlip and one washer should just be in light contact with the inner bearing race of the back bearing. At that point, if the housing is locked to the shaft, the pulling forces of the prop cannot pull the housing forward and "uncenter" the magnets (I think letting it do that will lose some of the effectiveness of the magnets).

AT this point, there may be some play on the inside of the housing between the housing and the inner bearing race. If you push the housing to the rear it might move a short distance and then rebound (if the shaft friction is not too high). To eliminate the play inside, the housing can be moved down the shaft a short distance. Or a spacer or spacers that are the thickness of the amount of travel can be placed on the shaft inside the housing.

It is OK to assemble these with all the play shimmed out, they will get longer as they warm so they won't tighten up. I would avoid a pre-load on the bearing though, just bring all the parts into a light touching contact.

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Yeah I've been using a 1/2" diameter piece of pvc pipe that's longer than the shaft pressed against the front (propeller) side to help coax the shaft out. This way only a short length of shaft has to bear the strain of being squeezed in the vise. I had problems doing it the other way around, with the pvc pipe on the back end of the housing. My shaft was bending as I compressed the vise due to its full length providing a better torque arm to bend itself with. Of course, this shouldn't have happened to begin with if I hadn't been so eager to fly that I skipped over cutting the shafts down to a proper length.

I have an assortment of pieces of metal tube, deep socket wrenches, etc., that I can use. The non-ferrous stuff is best of course. You can find some small aluminum spacers (cabinet hardware?) in the hardware section at like Home Depot. The ones that are #12 or 1/4" will clear the 4mm shaft and can be placed against the bearing so the shaft can be pressed down into it from the front.

A hole drilled with a 5/16" drill might just clear a 4mm shaft, 11/64" or #21 drill will clear it. If you have a metal plate on a piece of wood, drill a hole that size in the plate, you can rest the shaft end in the hole and press the shaft down into that.

QUOTE]So now that I've got the shaft flush against the housing, I need to find a tube that's <4mm to push the final bit of shaft out.

Thanks for that, It's for the good of the order in the long run, it will be your contribution to history and your legacy here. It is amazing and wonderful to be able to come here and be able to find images that date back 8 years or so. So often they are worth more than 1,000 words...

I couldn't find it now if my life depended on it, but I read a post in another thread where a guy said he ran his DT750 motors without the clips and washers. He said they were just fine that way.

I'm not sure I'd want to try it on a quad because if a motor separated, it would be a crash for sure, but maybe not on a plane. I find it pretty believable that it could be done though, because there seems to be a tremendous amount of magnetic force to overcome when you take one of these motors apart. I wonder if that force changes much while the motor is running?

I couldn't find it now if my life depended on it, but I read a post in another thread where a guy said he ran his DT750 motors without the clips and washers. He said they were just fine that way.

I'm not sure I'd want to try it on a quad because if a motor separated, it would be a crash for sure, but maybe not on a plane. I find it pretty believable that it could be done though, because there seems to be a tremendous amount of magnetic force to overcome when you take one of these motors apart. I wonder if that force changes much while the motor is running?

Rick

The prop can pull the magnet housing away unless the shaft is a tight enough fit to prevent it. The magnets resist the housing being pulled away also.

When it starts to lift the housing away, it also starts losing driving forces because of the shifted alignment between the magnets and the stator. So all things considered, you may be able to get away with it.

The stock shaft is about 1-5/8" to where the threads start, this shaft is slightly more than the right length if you are going to fit a prop saver as I showed at the link above, it already has the circlip groove and needs a flat for the housing grub screw:

I just did 4 motors with 4mm shafts from HK along with collets. They were straight with only 1 flat spot near the end and 64mm long. I pressed them in and ground a flat for the bell set screw and about 1/2inch stick out for the collets. After asembly with the bronze thrust bearing I made another flat spot for a drilled out wheel coller to the rear shaft portion. I allowed a slight movement in the setting. Excess shaft can be cut off. You have to search the length shaft you want. They were out of shafts with circlip grooves. I just worked around it.

The shaft will not be undersized and it will be no more that five ten-thousandths of an inch over sized. And that, along with the tolerances typical for bearing races, will give you the no play sliding fit to a light press fit in the races.

When ordered from Reid tool I did it by phone to place a small order (a few drill blanks). By doing that the lady that took the order set me up for a mail shipment (cheaper) instead of the (more expensive) UPS ground shipment that you get when you order online with the automated system.

Those drill blanks will be lacquered or have an invisible preservative coating on them when you get them. It is best to use like 400 or 600 grit emery cloth, dip them in light oil, spin them up in a drill motor (or use your lathe if you are a lucky dog) and take them down to bare and bright metal. Clean all traces of abrasive off, give them a light coat of oil, and either slide them or press them into place. The fit will be so good that it is almost orgasmic....

After struggling with these terrible headless grub screws, I started looking for a replacement. I noticed I had some M3x6mm hex head screws that came with my flamewheel 450 clone. These are a little longer than the stock grub screws, but seem to fit in the holes just fine. You can get a set of 20 for $1 shipped from rctimer:

You can even occasionally find 3mm screws in the small cardboard drawers assortments at hardware stores. Although 4mm and up is more typical of what you can find.

The parts racks at the LHS are a good source too, those 3mm button head screws are a Traxxas RC car part. Not nearly as cheap as the screws you posted but by the time you get those shipped from China the price will be up a little...

I trim screws like that to length by putting a nut on them and slicing the unwanted portion off with the Dremel tool and abrasive cutting disc. It only takes a few seconds and when you remove the nut it removes the burrs from the end of the screw.

All was working too well!
I hook my plane yeaterday on my last leg coming in for landing I was a tad too far and there she is now stock in top of the three at the highest possible point ~90' high..
I flew the hole day I had 10 Lipo's x 1300 mAh and 14 x 460 NanoThech that I made a plug to use 2 in parallel with a small connector.
The DAT 700 rewould perform the hole day without a glitch and now RIP unless a good gust of wind would have done miracle over night..
Today, I'll get another plane up using a stock original DAT 700 so I'll fell the difference for sure.
The name of the game is Fun!
Roger

That is a tough situation. I have had my share of planes in trees. I started out using a spin fishing pole. It worked well when there was no low bushes or trees nearby so I could get a good cast up and over the tree. I shot many old spark plugs up there. Some still hanging like Xmas ornaments. The idea was to get a fine fishing line over the offending branch or the plane. After getting to that point and the weight back to the ground I tie on a heavier 1/8 inch line and feed it over. Tie one end down solid and a nice stick on the other end nd pull like crazy, The branch will sway like in a wind storm and you may get it to fall to a lower branch or the ground. One time I sent up a heavy line afterwards and tied it to my truck hitch and broke the branch. Of course I was only 75 feet up on that one and 2 days to finally get it. If room allowed a surf fishing pole would make easy work of it with the heavier weight sinker and line. I have seen them cast here about 300 to 400 feet

I now use a slingshot. I have the new surgical type with wrist support. It is more accurate to shoot lines. I have a 4 inch bolt through the front Y with 2 nuts to jam against each other. I use a plastic spool of fishing line slipped on the bolt facing forward. This works like a spinning reel. Tie a couple of nuts on it and keep trying to fire over the target. I once got a friends plane after I shot through his wing. Your plane at 90 feet vertical it would be pushing the limit with 3 to 6lb fishing line. I wish I new someone that was a good archer. A much better chance of firing over

The Emmrod won't cast as far as a spinner, but it allows slingshot precise placement, which is key when it comes to hooking that one branch in the middle of a poorly maintained canopy. I like using tennis balls, since they have a predictable trajectory and are unlikely to damage the plane; they are also easier to manipulate in the branches (pull slow to get the ball to drop one branch lower, and give short tug followed with a hard pull to wrap the line around the target branch). Oh, and remember, sometimes you'll pull hard, the "lure" will suddenly break free, and you'll have whatever object you tied on the end headed toward your face at a high rate of speed. We've had laughs when the tennis ball whacked the operator in the head, but not sure how that would turn out if they were spark plugs.

I'm not sure if 90' high is possible with any fishing pole though... unless you use a potato gun or something. LOL! That would be fun, but depending where the tree is you may get a frown from local law enforcement. Other options would include like Neon's mentioned, a slingshot of some sort. Would also be cool to see a quad go up and place the line on the branch.